From 57f0f512b273f60d52568b8c6b77e17f5636edc0 Mon Sep 17 00:00:00 2001
From: André Fabian Silva Delgado <emulatorman@parabola.nu>
Date: Wed, 5 Aug 2015 17:04:01 -0300
Subject: Initial import

---
 arch/x86/include/asm/mutex_64.h | 127 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 arch/x86/include/asm/mutex_64.h

(limited to 'arch/x86/include/asm/mutex_64.h')

diff --git a/arch/x86/include/asm/mutex_64.h b/arch/x86/include/asm/mutex_64.h
new file mode 100644
index 000000000..07537a442
--- /dev/null
+++ b/arch/x86/include/asm/mutex_64.h
@@ -0,0 +1,127 @@
+/*
+ * Assembly implementation of the mutex fastpath, based on atomic
+ * decrement/increment.
+ *
+ * started by Ingo Molnar:
+ *
+ *  Copyright (C) 2004, 2005, 2006 Red Hat, Inc., Ingo Molnar <mingo@redhat.com>
+ */
+#ifndef _ASM_X86_MUTEX_64_H
+#define _ASM_X86_MUTEX_64_H
+
+/**
+ * __mutex_fastpath_lock - decrement and call function if negative
+ * @v: pointer of type atomic_t
+ * @fail_fn: function to call if the result is negative
+ *
+ * Atomically decrements @v and calls <fail_fn> if the result is negative.
+ */
+#ifdef CC_HAVE_ASM_GOTO
+static inline void __mutex_fastpath_lock(atomic_t *v,
+					 void (*fail_fn)(atomic_t *))
+{
+	asm_volatile_goto(LOCK_PREFIX "   decl %0\n"
+			  "   jns %l[exit]\n"
+			  : : "m" (v->counter)
+			  : "memory", "cc"
+			  : exit);
+	fail_fn(v);
+exit:
+	return;
+}
+#else
+#define __mutex_fastpath_lock(v, fail_fn)			\
+do {								\
+	unsigned long dummy;					\
+								\
+	typecheck(atomic_t *, v);				\
+	typecheck_fn(void (*)(atomic_t *), fail_fn);		\
+								\
+	asm volatile(LOCK_PREFIX "   decl (%%rdi)\n"		\
+		     "   jns 1f		\n"			\
+		     "   call " #fail_fn "\n"			\
+		     "1:"					\
+		     : "=D" (dummy)				\
+		     : "D" (v)					\
+		     : "rax", "rsi", "rdx", "rcx",		\
+		       "r8", "r9", "r10", "r11", "memory");	\
+} while (0)
+#endif
+
+/**
+ *  __mutex_fastpath_lock_retval - try to take the lock by moving the count
+ *                                 from 1 to a 0 value
+ *  @count: pointer of type atomic_t
+ *
+ * Change the count from 1 to a value lower than 1. This function returns 0
+ * if the fastpath succeeds, or -1 otherwise.
+ */
+static inline int __mutex_fastpath_lock_retval(atomic_t *count)
+{
+	if (unlikely(atomic_dec_return(count) < 0))
+		return -1;
+	else
+		return 0;
+}
+
+/**
+ * __mutex_fastpath_unlock - increment and call function if nonpositive
+ * @v: pointer of type atomic_t
+ * @fail_fn: function to call if the result is nonpositive
+ *
+ * Atomically increments @v and calls <fail_fn> if the result is nonpositive.
+ */
+#ifdef CC_HAVE_ASM_GOTO
+static inline void __mutex_fastpath_unlock(atomic_t *v,
+					   void (*fail_fn)(atomic_t *))
+{
+	asm_volatile_goto(LOCK_PREFIX "   incl %0\n"
+			  "   jg %l[exit]\n"
+			  : : "m" (v->counter)
+			  : "memory", "cc"
+			  : exit);
+	fail_fn(v);
+exit:
+	return;
+}
+#else
+#define __mutex_fastpath_unlock(v, fail_fn)			\
+do {								\
+	unsigned long dummy;					\
+								\
+	typecheck(atomic_t *, v);				\
+	typecheck_fn(void (*)(atomic_t *), fail_fn);		\
+								\
+	asm volatile(LOCK_PREFIX "   incl (%%rdi)\n"		\
+		     "   jg 1f\n"				\
+		     "   call " #fail_fn "\n"			\
+		     "1:"					\
+		     : "=D" (dummy)				\
+		     : "D" (v)					\
+		     : "rax", "rsi", "rdx", "rcx",		\
+		       "r8", "r9", "r10", "r11", "memory");	\
+} while (0)
+#endif
+
+#define __mutex_slowpath_needs_to_unlock()	1
+
+/**
+ * __mutex_fastpath_trylock - try to acquire the mutex, without waiting
+ *
+ *  @count: pointer of type atomic_t
+ *  @fail_fn: fallback function
+ *
+ * Change the count from 1 to 0 and return 1 (success), or return 0 (failure)
+ * if it wasn't 1 originally. [the fallback function is never used on
+ * x86_64, because all x86_64 CPUs have a CMPXCHG instruction.]
+ */
+static inline int __mutex_fastpath_trylock(atomic_t *count,
+					   int (*fail_fn)(atomic_t *))
+{
+	if (likely(atomic_cmpxchg(count, 1, 0) == 1))
+		return 1;
+	else
+		return 0;
+}
+
+#endif /* _ASM_X86_MUTEX_64_H */
-- 
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